Directional drilling is frequently performed with fluid-powered downhole motors. The fluid-powered downhole motor is run-in on a tubing string which can be made of joints which are run-in from the surface in sequence. At the conclusion of the operation, the process is reversed. In order to put together the tubing string with the downhole motor so that the motor can be spotted in the appropriate location or advanced during the drilling operations, allowances have to be made for filling or emptying the tubing string as the tubing string is enlarged or shortened, respectively. That is, as additional stands are connected at the surface and run downhole, fluid in the wellbore needs to be admitted into the tubing string to prevent a pressure imbalance on the tubing string which would tend to put a collapse force on it. In essence, the bypass valve located adjacent the downhole motor admits well fluids into the tubing string as additional stands are added at the surface. Similarly, when the process is reversed, hydrostatically pressured fluid in the tubing string above the downhole motor drains into the wellbore as stands are removed from the top of the string.
Bypass valves have been used in the past which when in the open position, allow fluid communication between an annular space around the tubing string and the tubing string to facilitate filling and/or draining the tubing string during the operations of running in or tripping out of the hole. These bypass valves were designed to close if flow under pressure was applied in the tubing string so as to allow the downhole motor to operate. These valves presented reliability problems, primarily due to undesired leakage, which lessened the performance of the downhole motor. Accordingly, they have fallen into greater disuse due to their unreliability.
One such known bypass valve design is illustrated in FIGS. 1 and 2 of this application. A tubing string (not shown) is connected to the bypass valve 10 at thread 12. Inside of bypass valve 10 is a central bore 14 in communication with a sliding sleeve 16. Sleeve 16 is biased by spring 18 to the position shown in FIG. 1. In the FIG. 1 position, openings 20 are in fluid communication with annular space 22, which is in turn in communication with outlets 24. In the position shown in FIG. 1, the pressure drop without flow or with low flow across the sleeve 16 is insufficient to overcome the force of spring 18, and the sleeve 16 stays in the open position, allowing flow, represented by arrows 24, to go in either direction through openings 20. Below the lower end 26 of sleeve 16 is a seal bushing 28. Cylindrical seal surface 30 on sleeve 16 is pushed into bushing 28 when the spring 18 is compressed due to applied fluid pressures in bore 200 of sleeve 16. This position is illustrated in FIG. 2. At the lower end of the bypass valve 10 is thread 32 to which is connected a tubular 34, which ultimately supports the downhole motor (not shown).
Those skilled in the art will appreciate that rather than having a cylindrical sealing surface 30 being forced into a bushing such as 28, the body of the bypass valve 10, in the area of bushing 28, can have one or more O-rings and grooves or, alternatively, the cylindrical surface 30 can accommodate O-ring grooves and O-rings and have those rings forced into a seal bore which would be in place of the bushing 28. Regardless of the configuration, whether as shown in FIGS. 1 and 2, or through the use of O-rings, the problem of reliability of the seals has arisen. The primary reason for the problem is that the sealing medium, such as the seal bushing 28 of FIG. 1, is adversely affected by sharp corners, such as the edges of the openings 20 and the sharp corners 36 found at the lower end 26 of the sleeve 16. Grit in the mud is another source of potential seal problems. Another problem is that as soon as there is some sealing contact, such as between surface 30 and bushing 28, a differential pressure develops across the point of contact which further aggravates the interaction of sharp corners, such as 36, with the bushing 28. In essence, a shearing force acts across the seal which, if it is an O-ring, can rip it or yank it out of its groove.
For these reasons, the designs in the past, as shown in FIGS. 1 and 2, have proven not to be reliable and have gone into relative disuse. The absence of a bypass valve presents difficulties in tripping in and tripping out. While tripping out, a bypass valve is important so that fluid can drain back into the wellbore as stands are removed at the surface. Without such a bypass valve in the wellbore, when joints are unthreaded at the surface and if they're still full of mud, the mud will spill all over the rig floor. This creates environmentally unacceptable situations, particularly in offshore applications using oil-based muds. Without the bypass valve, each stand, as it is pulled out, is still full of mud which will spill out on the rig floor when a joint is broken. In running in, the bypass is important to allow the additional stands that are added to the string to fill as they are added. With no bypass valve, filling has to be done manually after every so many stands have been added to the string. If filling is not done manually and no bypass valve is operational to fill the string automatically, hydrostatic differential pressures can exist on the tubing which unduly stress it, possibly to the point of collapse if allowed to go uncorrected. Thus, in the past, operators have manually filled the string every 10 joints. This is a cumbersome procedure that takes time which creates cost for the operator.
Accordingly, the object of the present invention is to provide a reliably operating bypass which eliminates the design flaws of the prior art and presents, in a compact design, a valve which can reliably allow bi-directional flow until applied pressure from the surface closes it for operation of the downhole motor. Another objective in increasing the reliability of the bypass valve is to prevent dragging sealing members past sharp corners and to employ the pressures already existing in the valve for a boost force to ensure proper sealing once the sealing members have contacted. These and other features of the invention will become apparent to those skilled in the art from a review of the specification below.
Of general interest in the area of seals are U.S. Pat. Nos. 2,495,011; 4,256,314; 4,258,925; and 5,295,534.